The production of semiconductors into various types of integrated circuits, displays, memories, sensors and other devices typically requires that contaminating particles be minimized. In many cases the presence of contaminating particles can cause defective operation, performance problems, or render the device inoperable.
It has previously been typical for silicon wafers to be processed using a method commonly referred to as the "RCA clean". In this process the silicon wafer, substrate, or other item is first cleaned with an aqueous solution of sulfuric acid and hydrogen peroxide to remove organic contaminants. This is followed by treatment with an aqueous solution of ammonium hydroxide and hydrogen peroxide. After this the wafers are rinsed with deionized water.
The RCA clean also typically involves stripping the silicon dioxide layer formed in the previous steps using an aqueous hydrofluoric acid solution. The hydrofluoric acid solution removes the silicon dioxide layer leaving bare silicon. The bare silicon demonstrates the property of not being easily wetted and is frequently referred to as being "hydrophobic". This should be contrasted with the silicon dioxide surface existing prior to this step, which is easily wetted and the wafer is commonly called "hydrophilic".
The hydrofluoric acid oxide removal step is typically followed by a short rinse in deionized water. The rinse is kept short to minimize silicon dioxide formation. The rinsed wafer is typically not dried.
The RCA clean method also typically includes transferring the wet wafer from the previous step into an aqueous solution of hydrochloric acid and hydrogen peroxide. This step is designed to dissolve metals.
Although this sequence of processing steps is widely used, it is recognized that the process is of limited effectiveness for removing surface adhering particles. The effectiveness is limited to a certain level of particle contamination dependent upon prior processing and the level of cleanliness existing on the wafer when the cleaning process is begun.
The cleaning of semiconductor surfaces has great economic significance because of the volume of integrated circuits and other semiconductor devices being produced, and the significant percentage of processed semiconductor devices which are rejected due to defects caused by particle contamination. Particle contamination is also of great significance because of increased facilities and equipment cost, and costly and time-consuming procedures used in an effort to prevent particle contamination. It is generally recognized that contamination must be prevented because it is often difficult or impossible to adequately remove contaminants once contamination has occurred.
Thus there has long remained a need for improved cleaning processes which are effective at removing particulate contaminants from the surface of silicon and other semiconductor materials.